Comment 4 for bug 17763

Another user with the same issue:
http://www.ubuntuforums.org/showthread.php?t=40845

They suggest that it's a video problem (that occurs during heavy I/O, only in
X). Like the poster, I require my video card to do hardware acceleration & 3D.
I too have upgraded to the nvidia driver

He has a completely different video card than I, and a different Motherboard and
processor. This sounds like a problem with X in Kubuntu.
(I have successfully installed an older version of Ubuntu on my system, without
this problem)